It is desirable and sometimes necessary to sense the positions of various devices that can assume multiple positions. One such device is the door of an automobile. The latches of such doors typically have half-latch and full-latch positions. When the door is in the full-latch position, the latch is fully engaged and the door in its fully closed position. When the door is in the half-latch position, the door in not in its fully closed position but the latch is sufficiently engaged to prevent the door from opening without further intervention by an operator. When the door is in neither the full-latch position nor the half-latch position, the door is open.
There are several reasons to sense these door latch positions. For example, the driver of an automobile can be notified when a door is in the full-latch position, or is in the half-latch position, or is open. Alternatively, power assist doors are being contemplated in which a motor or actuator is used to pull the door tightly closed to, for example, better shut out exterior noise. In this case, it is desirable to sense the half-latch position of the door in order to energize the motor so that it pulls the door to the full-latch position, and to then sense the full-latch position in order to prevent further pulling by the motor.
Hall sensors have been used to sense the position of objects by detecting the presence or absence of a magnetic field. Thus, a small magnet may be attached to an object whose position is be sensed, and the magnetic field of the magnet is detected by the Hall sensor in order to determine the position of the object. If the circuit that processes the signal from the Hall sensor is configured for uni-polar operation and has a digital output, the sensor will turn on when the magnetic field from the magnet exceeds a pre-defined threshold and will be off the rest of the time (ignoring the effects of hysteresis). Therefore, the circuit will only be able to detect when the object is in a certain discrete position.
In applications requiring the detection of multiple positions, such as the automobile door application discussed above, an encoded signal is frequently utilized. However, if only one Hall sensor is to be used to detect multiple positions, a complex time based extrapolation algorithm is required to determine the multiple positions.
To avoid the use of such an algorithm, a separate discrete Hall sensor can be used to detect each of the various positions of the object. However, the use of multiple Hall sensors increases the cost of the position detection system. In high volume industries such as the automobile industry, the cost can become significant.
The present invention relates to a multiple position sensor that overcomes one or more of these or other problems.